The present invention relates to air temperature control systems of the central type used in buildings, and more particularly to methods and apparatus which utilize colder outside air to reduce the temperature of the interior air, particularly in large multi-room buildings.
Generally, a conventional air conditioning system installed in a large building employs water circulated through a closed conduit system inside the building having induction unit coils or heat exchangers located along the perimeter of the building or elsewhere to cool recirculated room air to the desired temperature. In such systems, the coolant in the refrigeration unit, which is used to chill the room air perimeter cooling liquid by heat exchange, is in turn cooled by heat exchange with a separate liquid circulated through an entirely separate series of conduits to an air cooling tower usually located on the roof of the building. As is well known in the art, in the conventional air cooling tower spraying means are employed which cause the liquid to be cooled by direct contact with the outside air. As is also well known, since the cooling tower acts as an air scrubber, the liquid picks up all kinds of contaminants and corrosive substances from the pollutants in the air which, if introduced into small conduits such as are found in the induction units inside the building, could cause serious damage due to corrosion, scaling, clogging and the like. Thus, in the conventional air cooling system three separately circulated fluids are generally used: the chill water circulated inside the building in a closed conduit circuit for cooling the room air, the coolant circulated in the refrigeration unit for chilling the cooling liquid, and solely as an adjunct to the refrigeration unit, the cooling tower liquid which is circulated in an open large conduit circuit through an air cooling tower outside the building for cooling the refrigeration unit cooling medium.
With such conventional cooling systems, the refrigeration unit is in substantially continuous year round operation even when the outside air temperature is at or below the desired room temperature. This is required because the interior of the building is effectively insulated from the cold outside air while the perimeter room air is heated by radiation energy from the sun. In addition, the air induction units used to recirculate the room air, and the electric lights, generate substantial quantities of heat which heat up the room air still further. As a result, conventional systems cause substantial consumption of electrical energy and/or steam energy depending on whether the refrigeration unit is electrically or steam driven.
Elimination of the refrigeration unit by utilizing a heat exchanger instead to provide heat interchange directly between the liquid in the cooling tower conduit circuit and the chill water in the interior conduit circuit would not effect significant economies. Apart from the high initial cost of building and installing such a heat exchanger, such a system would have only marginal utility due to inherent capacity limitations and heat losses.
In the conventional practice, during extremely low outside air temperature, for example below about 30.degree.-35.degree. F, the building is placed in a heating mode. The refrigeration unit is shut off and the perimeter or secondary water is circulated through a steam heat generator unit where the water is heated to approximately 100.degree.-140.degree. F and circulated through the same induction unit coils providing heat for the rooms. Where limited cooling is required, this is obtained by closing off the induction unit coils to the hot water and introducing outside air into the induction units in those rooms which are warm. However, air which is transmitted over several hundred feet will absorb the heat, raising its temperature as much as 10.degree.-15.degree. F, and therefore will not have much cooling effect. Furthermore, friction heat losses in the fan unit will also produce up to a 5.degree.-15.degree. F rise in temperature of the air. Thus, attempts to use cooler outside air for cooling purposes, particularly during the intermediate seasons, have had but limited success.
It is an object of the present invention to reduce the energy consumption in central air temperature control systems of the type described above.
It is a further object of the invention to provide a central air temperature control system which significantly reduces or eliminates the need for energy-consuming refrigeration units during the cooler periods of the year by effecting cooling via the outside air.
It is a still further object to provide such energy conservation with minimal changes to conventional air temperature control systems.
Briefly, the foregoing objects and advantages are accomplished in accordance with the present invention by circulating a single liquid cooling medium having suitable chemical properties between the perimeter or other room air heat exchangers inside the building and an air cooling tower outside the building when it is cold enough outside for the cooling tower to bring the circulating liquid to an effective cooling temperature below the interior air temperature, preferably at or below the desired temperature for the room air, and still more preferably at a predetermined liquid temperature desired for cooling at the room heat exchangers. The water is subjected to spraying in the air cooling tower process where it is brought into direct cooling contact with the outside air and is preferably cooled to substantially the outside wet bulb air temperature. Suitable filtering means, preferably mechanical, are employed to remove contaminants before the liquid is introduced into the interior circuit. In one preferred embodiment, contaminants having a particle size generally greater than about 5 mils to about 10 mils in diameter, which may be picked up in the air cooling tower, are removed. When the temperature of the liquid leaving the cooling tower is below that desired at the induction units, portions of the return cooling liquid are caused to bypass the cooling tower and are mixed with the air cooled medium in suitable proportions to provide the desired liquid temperature for cooling.
Advantageously, existing conventional systems can be converted to practice the invention. Preferably, the cooling tower is adapted to cool the liquid introduced thereto substantially to the ambient wet bulb air temperature. Bypass conduits are installed with appropriate valving and filtering means to connect the conduits of the open condenser liquid circuit directly into the interior normally closed liquid circuit so that the refrigeration unit can be bypassed as may be desired during operation. Of course, it will be evident to those of ordinary skill in the art that the circulating liquid must be made compatible for use in the combined system by suitable chemical treatment to prevent corrosion, scaling and the like.
With such an arrangement, not only is the refrigeration unit taken out of operation during substantial portions of the year, but the number of pumping units in operation is also reduced because only a single fluid conduit circuit is employed instead of the three separate conventional circuits. When the temperature of certain rooms must be raised slightly, the cooling liquid is prevented from circulating through the induction unit coils in the rooms and air from the rooms is recirculated through the air induction system and is heated by the heat of friction generated by the fan unit. While such use of the recirculating air to heat is not new, its energy saving advantages have in the past been limited. When the building is in the cooling mode during periods when the outside air is below the desired interior air temperature, the wasted energy involved in running the refrigeration machine cancels out any savings resulting from the use of recirculated air to provide limited heating. When in the conventional system the refrigeration machine is shut off to conserve energy and heated water is circulated in the heating mode, the heat energy in the recirculated air becomes superfluous and is wasted. Thus, heat energy normally constituting heat loss in conventional systems is advantageously put to use with commensurate further savings in energy due to reduction in operation of steam heat generating units and the like.